The actual fluorosis prevalence value reported for a population can vary considerably among different scoring systems and within a scoring system due to intrinsic factors defining a case. Currently popular scoring systems evaluate the level of fluorosis are based on different measurement units, diverse numbers of sites per person, and distinctly different groupings of clinical symptoms. Intrinsic factors for a scoring system include the inclusion of a questionable category, together with both the level of fluorotic involvement and the number of sites within a subject required for case definition. None of these factors are related to the level of fluoride exposure in the examined population. Case definitions for each scoring system are desirable, essential for obtaining prevalence estimates, but currently not available for all scoring systems. Dean's scoring system has been the most widely used, includes a case definition, and thus, despite its peculiarities, will probably continue to play the role of reference standard. Ratios of fluorosis prevalence magnitudes, as evidenced by odds ratios, can be more stable between scoring systems for comparing groups having different fluoride exposure levels. There is a strong correlation among extent and specific measures of fluorosis severity for the DI and TSIF scoring systems, as well as within each scoring system separately. Parallel patterns in fluorosis severity were found among groups exposed to different levels of fluoride. The effects of fluoride exposure are best understood using relative measures contrasting severity levels of fluorosis for two or more fluoride exposure levels.